The increasing use of polymers in place of the more traditional types of structural materials (e.g. wood, metals, etc.) has necessitated the compounding of such polymers with a variety of stabilizers in order to enhance the ability of such polymers to withstand prolonged exposure to a variety of degradative forces. Degradation of such environmentally sensitive polymers can be caused by exposure to light, heat and/or air. Such degradation is usually manifest by either a partial or total loss of structural integrity, changes in light transmission properties, changes in color, loss or reduction in flexibility and/or resiliency, or any combination of the above phenomenon. As will be appreciated, the stabilizers which are used in conjunction with the above polymeric materials, in addition to providing protection against such degradative changes, must also be compatible with the aesthetic properties of the polymeric article and be effective at low concentrations. The economics of the marketplace dictate that these stabilizers be relatively inexpensive and capable of preparation from readily available starting materials by simple and straightforward synthesis techniques.
The diazacycloalkanones have been found to be highly effective in the stabilization of polymeric materials against the photodegradative forces of ultraviolet light. The efficacy of such materials in the UV stabilization of polymers is described in U.S. Pat. No. 4,190,571, the disclosure of which is herein incorporated by reference. Specifically, the '571 patent teaches the preparation of 2-keto-1,4-diazacycloalkanes, such as 1-propyl-3,3,5,5-tetramethyl-2-piperazinone, by reaction of an appropriate 1,2-diamine with acetone cyanohydrin in the presence of sodium hydroxide and benzyltriethylammonium chloride. The crude reaction product is typically distilled to yield the purified substituted-piperazinone product. U.S. Pat. No. 4,297,497, which is incorporated by reference, teaches the synthesis of related 2-keto-1,4-diazocycloalkanes by reacting a 1,2-diamine, a monoketone and haloform in the presence of alkali and phase transfer catalyst, and subsequent distillation to obtain the purified product.
The present invention relates to the purification of a novel class of 1-(2-amino-2-alkylpropyl)-3,3,5,5-tetraalkylpiperazinones. The novel compounds are prepared by reacting an appropriate 1,2-propanediamine with a ketone and a haloform in the presence of alkali as described in U.S. patent application Ser. No. 664,901, filed Oct. 26, 1984, now U.S. Pat. No. 4,547,538. This reaction yields a crude reaction product having a 75-85% purity. For practical applications, the crude reaction product is separated from the aqueous layer and purified by fractional distillation, which results in a maximum purity of about 90% and the formation of undesirable side-products. Through this invention, it was unexpectedly discovered that if the fractional distillation was carried out in the presence of an inorganic base, a product having a purity as high as 96% was obtained while suppressing the formation of undesirable side-products.
It is the object of the present invention to provide an improved process for purification of the substituted amino-alkyl-piperazinones comprising fractional distillation in the presence of an inorganic base. These piperazinones are useful as UV stabilizers and as intermediates for preparing a variety of high molecular weight polymer stabilizers.